Gas detection



July 1l, 1950 J. E. BLISS Er Al. I 2,514,690

GAs DETECTION Filed Aug. 2s, 1946 IN VEN TORS Patented July 11, 1950 GASnE'rEc'rIoN Jack E. Bliss and Olin R. Prather, Midland, Tex.,

assgnors to Rotary Engineering and Manufacturing Company Inc., Midland,Tex a corporation of Texas Application August 26, 1946, Serial No.693,157

(Cl. 'I3-26) 16 Claims. l

This invention relates to a method of and apparatus for gas detection,as during the drilling of wells and the like.

Previously, it has been diicult to determine with exactitude thepresence of oil, and particularly of gas, encountered during thedrilling of a well, wherein a drilling bit is normally attached to thelower end of a rotating hollow tube or drill pipe, and the bit drills ahole considerably larger than the drill pipe, so that an annular passagebetween the outside of the drill pipe and the inside wall of the well isformed. In the usual drilling procedure, quantities of mud or drillingfluid are pumped down through the pipe, to be discharged throughsuitable apertures in the drill bit. This mud carries the removed rock,shale, sand or the like, upwardly in the well through the annularpassage, and is recirculated through the well in what may be termed themud circulating system. Mud is normally a, suspension of clay or othermaterial in water, with suitable materials added to control theproperties of the mud. For instance, bentonite may be utilized to governviscosity and gel of the mud, barium sulphate may be used to increasethe weight of the mud, tannic acid may be used to thin the mud, andcaustic soda may be used to raise the pH value. There are, of course,other additives and control agents utilized for other purposes, or\\ inlieu of one or more of the foregoing. Some success has been achieved bytesting the outgoing mud for detection of oil or gas, but suchoperations are nowhere near uniformly successful, for several apparentreasons.

Due to the relatively large quantities of mud utilized, the cuttings, ormaterial removed by the drill, are relatively widely dispersed, and oilor gas, when encountered, may not be present in suicient amounts to bedetected. Thus, when a stratum of oil or gas bearing sand or formationonly a few feet thick is drilled through, little oil or gas may escapeinto the mud, and the amount thereof is usually so dispersed through themud that detection is diiilcult. Furthermore, the pressure of the mud isusually maintained considerably above the normal hydraulic pressure atthe depth being drilled, and there may be very little escape of oil orgas into the well, and consequently little opportunity for the drillerto know of the presence thereof. There is a further possibility that agas or oil pocket may be sealed by the mud under pressure being forcedinto the formation with the result again that very little oil or gas mayescape into the mud.

In addition, when oil or gas is detected in the 2 outgoing mud stream itis often difficult and sometimes impossible to determine the point atwhich the oil or gas entered the well. The time required for the mud topass from the top of the hole to the bottom and back upwardly again,even though the inside of the hole may be ragged and uneven, can bemeasured by placing a suitable indicating material in the mud and al-.lowing it to travel down through the pipe and then back up through thehole. Also, the interior volume of a drill pipe and the pumping rate andpump volume are known, so that the time required for the mud to traveldown the drill pipe can be ascertained. By simple subtraction, the timelag between the position of a specified lportion of the mud at thebottom of the hole and its appearance at the top can be determined.Also, the length of the drill pipe is known, as is the drilling rate.Thus, the depth at which a specific portion of the outgoing mud passedthrough the bit can be determined, and the condition of the mud willtend to reflect conditions at the depth being drilled, subject tocertain inaccuracies which are of extreme importance. For instance, ifthere is a gas-bearing formation at, say 2,000 ft., and the well is downto 4,000 ft., gas may continue to bleed into the mud from the formationat 2,000 ft., so that the operator cannot determine whether the gas iscomingl into the mud from the bottom of the well or somewhere along theside of the well. Oil may bleed into the mud during its travel upward inthe well in the same manner. Also, oil and gas are often recirculatedseveral times around the mud circulating system, and this causes falseoil or gas indications or shows to be logged or recorded. Thus, theremay be indications of oil and/0r gas in the mud over a considerabledrilling depth,but such oil or gas may be coming from only one position,and that position may be considerably removed from the bottom of theWell. Also, if short sand beds, for instance, are encountered and theseare oil or gas bearing, it is diiicult to determine for some time thethickness of the bed, since the subsequent mud may receive oil and/orgas therefrom, long after the bed is passed. Consequently. the methodsnow in use for determining the presence of gas, for instance, byanalysis of the mud, may give an accurate indication of the gas contentof each specific portion of the mud, but there is no assurance that thegas was received by the mud at any particular depth, once a gas bearingformation has been encountered somewhere during the drilling of thewell.

Among the objects of this invention are to provide an improvedl methodfor detecting the presence of gas in substrata encountered during welldrilling; to provide such a method Whichis not affected by dilution ofgas'in mud; to provide such a method by which the exact location of gasbearing strata can be determined; to provide such a method by whichrelatively minute quantities of gas can be detected, irrespective ofdiffusion of gas into the mud, or gas i'ecirculated in the mud stream;to provide such a method which does not interfere with the normal welldrilling operation; Vto provide such a method which is relatively simplein operation and may be carried out relatively rapidly; to provideapparatus particularly adapted to carry out the above method; and toprovide such apparatus which is readily portable, .easily operated, andinvolves a minimum of equipment. Other obiects and the novel features ofthis invention will become apparent from the description which follows.

In general, the method of this invention consists in separating thecuttings from the mud, and then testing the cuttings as hereinafterdescribed; to ascertain the possible presence of gas therein. It isadvantageous to test the cuttings for oil as well as Ior gas, so thatmore complete information about the well will be available. Preferably,in testing ior the presence oi' oil, a selected group ol" cuttings issubiected to ulti-a violet radiationv or tile like, and carbontetrachloride or other suitable solvent is utilized in obtaining aresidue ring as described hereinafter in greater detail. Fluorescence ofthe residue ring indicates the presence of oil, since some of theparticles which iluoresce may be mineral and naturally uorescentparticles, but the removal of the oil by the solvent from the particlesand subsequent deposition of the oil in a residue ring enables thestarting to arrive at the surface.

contains air and leads back to thev container, the

,l circulating and recirculating air thereby picking may be producedinitially in the closed path exteriorally of the container, before thecontainer is closed, sov that when the container is connected to theclosed path, the vacuum in the latter will tend to draw air from thecontainer. While such an initial vacuum may have some effect in causingthe above methods of this invention is illustrated in the accompanyingdrawing, in which:

Fig. 1 is a side elevation, with certain portions in section and othersshown diagrammatically, of apparatus constructed in accordance with thisinvention;

Fig. 2 is a vertical cross section of a container. forming a portion ofthe apparatus of Fig. 1, but provided with a mechanical agitator; y

Fig. 3 is a fragmentary side elevation, similar to Fig. l, illustratinga modification thereof and Fig; 4 is a fragmentary vcross section of acolor reaction plate, illustrating the position o f the cuttings and theresidue ring after the solvent treatments in testing for oil ancillaryto this invention.

In carrying out the method of this invention, the cuttings-which areparticles of rock or the like, cut by the bit and circulated to thesurface of the hole--are separated from the mud by a vibrating orrotating screen or the like. It is necessary, of course, to know theexact depth in the well the cuttings involved came from, and it isconvenient for this purpose to provide a 25. clock which is set behindby a predetermined time,

i. e. the time lag or time necessary for thecuttings to ow from thebottom up to the top of the well. The time lag may be determined in themanner previously indicated, i. e. by timing the passage of strips ofcellophane or brick chips or the like from the top to the bottom andthen back to the top, and subtracting the calculated time for passagefrom the top to the bottom, based on the flow rate of the mud and theknown volume of the pipe. A well log is generally kept, and the lengthof the drill string is always known. Thus, a first clock, set to correcttime, is used in charting the well log, while the second clock is setbehind the first by the time lag of the cuttings. For instance, the bitmay reach 4,000 ft. at 4:00 p. m. by the rst clock and at 4:15 p. rn.reach 4,002 ft. Now, if the lag time is 30 minutes, the second clockwould have indicated 3:30 p. m. when the bit reached 4,000 ft. and 3:45p. m. when the bit reached 4,002 ft. Thus, when the second clockindicates 4:00 p. m., the cuttings from this 2-foot interval (i. e.between 4,000 ft. and 4,002 ft.) are A fine mesh screen or othersuitable receptable is then placed in the mud stream tov catch thecuttings. When the second clock reaches 4:15 p. m. the cuttings fromthis 2-foot interval should all have reached the surface and bedeposited on the screen or other receptacle.

After separation, a portion of the cuttings may be rinsed in Water andsubjected to an ultra violet light test for the presence of oil; Thismay consist in first plalcing the cuttings in a position in which ultraviolet light from a suitable source,

no such as a lanip or the like, and in a dark room the release ofgasfrom the cuttings, it is often 'u or darkened enclosure, is projectedonto the cuttings. The fluorescence which may .result may be due-eitherto the presence of oil, or mineral particles, such as limestone, whichhave the property of iluorescing under ultra violet light. Thepercentage of the sample which fluoresces may be estimated and recorded,for later use.

A number of the pieces which uoresce mayv then be pickedv out and placedin a color reaction plate, such as plate P of Fig. 4, the set ofcuttings 9 being placed in a thumb hole I0. A representative or averageset of the cuttings may also be'placed in another thumb hole, such setincluding iluorescing and non-fluorescing pieces in about the sameproportion as the sample. Each set of cuttings is then subjected to anoil solvent, such as ether, acetone, or the likebut preferably carbontetrachloride. The solvent will tend to dissolve out oil, if present inany of the cuttings. and the reaction plate with its quantity ofcuttings is permitted to stand until the solvent evaporates. Sometimes asecond application of solvent is applied, particularly if the cuttingsare wet and the first application of carbon tetrachloride merely tendsto remove moisture. When oil is picked up by the solvent, the oil isdeposited as the solvent dries, particularly in the form of a residuering II, as in Fig. 4, around the edge of thumb hole I0. The ultraviolet light test will disclose the presence of such a ring, whichindicates that there was oil in the sample. In the case of the set ofcuttings which includes only particles which were fluorescent initially,after the applied solvent evaporates, the presence of a fluorescent ringindicates that at least a portion of the original fluorescence was dueto oil. If no ring is left after the solvent evaporates, this is anindication that the original iluorescence was due to minerals. If thefluorescence is due to oil, then the percentage of the sample whichshowed original fluorescence is recorded and plotted as such, that is, acurve indicating percentage of sample showing oil fluorescence isplotted on the g. If the fluorescence is mineral fluorescence alone,such as occurs in the case of most limestone formations, no recordingris necessary.

A second oil curve is also plotted on the log. This curve indicates therelative amount of fluorescence of the oil ring deposited, and, inproportion, the relative amount.of oil present in the cuttings at thetop of the hole. If it appears that the cuttings are about 100 per cent.representative of the formation being drilled (that is, that nomaterial, such as shale, is sloughing in from higher in the hole) thecompositeor representative sample is used to obtain the second oilcurve. If it appears that some of the sample is shale which has sloughedinto the hole from above the bit, the selective sample, i. e. thatcontaining only particles initially fluorescent, is used to obtain thesecond oil curve. In other words, shale or the like sloughing into thehole from above the bit, should be disregarded. It should beunderstoodmf course, that in evaluating the results of testing inaccordance with this invention, such results should be correlated withother data, such as the type of strata through which the well passes,previous experience in such strata, the depth and type of bed, and othergeological considerations.

After testing for oil in the manner above indicated, or simultaneouslytherewith, another sample of the cuttings is tested for gas inaccordance with this invention. For this test, a suitable container,such as container I2 of Fig. 1, may be filled about half full with clearwater, or other suitable liquid, and then sufcient cuttings placedtherein to bring the water level up to about approximately thethree-quarter mark, such as to the level I3 or I3 of Figs. 1 and 2,respectively. The container I2 may have a convenient capacity, such asabout one quart, and after the cuttings are placed therein, the top I4is attached thereto in a conventional manner. Two connections may beprovided in top I4, i. e. an outlet connection I5 having a valve I6associated therewith, and an inlet connection I1 having a valve I8associated therewith. From inlet connection Il a pipe 26 extends nearlyto thebottom of container I2 when top I4 is in place. A vacuum may beproduced in the interior of container I2, and more particularly air and/or an air-gas mixture circulated through the chamber vand through thecuttings by an air compressor 20, which is connected by a suction tube2| with valve I6. It will be understood, of course, that a vacuum pump,or even an air circulating impeller operating on the blower principle,may be substituted for the air compressor 20. discharge from compressor20 passes through a tube 22 to a housing 23 for a detector illament 24,which is the hot leg of a gas detection bridge circuit. The air orair-gas mixture is returned to the cuttings through a return tube 25,connecting housing 23 with valve I8, and recirculation pipe 26 extendsfrom connection I1 nearly to the bottom of container I2, forrecirculating air and/or an air-gas mixture around the cuttings.

In operation of the gas detection circuit, as in Fig. 1, a voltage of apredetermined amount, such as one volt, is impressed across detector arm28 of the bridge by a battery 29, a switch 30 being utilized in turningthe current on and off, and a variable resistor 3I being used to adjustthe voltage. The lower arms 32 and 33 of the bridge circuit are providedwith fixed resistors 34 and 35, respectively, while the upper armscomprise the detector arm 28 and a compensator arm 36 in which isinstalled a compensator filament 3l, which is preferably the same sizeand has the same characteristics as detector filament 24. The detectorand compensator filaments may be of the activated platinum type normallyused for gas detection purposes in mine safety work. A suitable detectorand compensator unit for use in this invention is No. DT-'16363,supplied by the Mine Safety Appliance Company, the filaments beinginstalled in a dual housing.

The bridge also includes a galvanometer 38, connected across the upperand lower arms, and to a potentiometer 39 for adjusting the galvanometerto a zero reading when air alone is passed through the detector housing23, prior to its use for gas detection. A voltmeter 40 may be connectedbetween one end of the bridge and the galvanometer 38, either on thedetector side or on the compensator side, as shown. The latter ispreferable because when the resistance of detector filament 24 begins tochange, due to the presence of combustible gas, the voltage does notalways remain constant on the detector side.

To start the test, tubes 2l and 25 are disconnected and air alone passedthrough detector housing 23, to adjust the bridge into balance. Tubes 2land 25 are then connected to valves I6 and I8, respectively, and valveI8 may be closed and valve I6 opened, so that a vacuum of a vdesireddegree, such as 4 to 5 in. Hg, may be produced in the container. ValveI8 is then opened, so that the air, or mixture of air and any gaspresent, passes through housing 23 and recirculates through the chamberformed by container I2. The air, or mixture of air and gas, bubblingfrom the lower end of pipe 26, passes repeatedly over the cuttings incontainer I2, thereby causing additional gas to evolve from the cuttingsand pass into the air.

The evolution of gas from the cuttings may be enhanced by agitating thembefore and/ or during the passage of air thereover, as illustrated inFig. 2. Thus, the container I2 of Fig. 2 is identical with the containerof Fig. 1, but an agitating impeller 45 is mounted in the lower portionof the container, being suspended at the The 1 lower end of a shaft tube46 and rotated by a motor 41 mounted on top I4 of the container. Ifdesired, the'agitating device may be mounted in the base of thecontainer, in a customary manner. It has been found that the agitationoften reducesfconsiderably the time required to obtain a satisfactoryreading from gas containing cuttings. The apparatus of Fig. '2 isotherwise identical with that of Fig. 1, the air compressor orcirculator and bridge circuit being the same.

As soon as the circulation and recirculation of air through thecontainer, preferably over the cuttings, and then through the detectorhousing 23 begins, galvanometer readings can be taken. It is sometimes amatter of several minutes before any observable reading is obtained, andit may be necessary to let the cuttings set awhile, as for three or fourminutes, and then repeat the test. The circulation and recirculation ofthe air, or air and gas mixture, is continued until the maximum gasreading is secured by means of detector filament 24, or the operator iscertain that there is insufhcient gas present to be worth while.

Normally, while the vacuum initially caused evolution of gas, in manyinstances it has been found that very little or no vacuum is necessaryto obtain suicient gas from gas bearing cuttings to obtain asatisfactory reading. Thus, the passing and bubbling of air over thecuttings and the recirculation of the same air, or gas-air mixture, withconsequent increase in the proportion of gas, enables a sufficientproportion of the gas to be extracted from the cuttings. When it isunderstood that at a depth of, say 6,000 ft., the hydraulic pressureproduced by the mud may be on the order of 3,000 lbs. per sq. in., andwhen the cuttings reach the surface so that the pressure is reduced toatmospheric, a considerable portion of the gas will have escaped, due tosuch reduction in pressure, the extraction of the gas from the cuttingsby the passage of air thereover, and the recirculation of the air, whichis maintained at as small a volume as possible, in accordance with themethod of this invention, is all the more remarkable. The prior art hasconsidered that the extraction of gas from cuttings (as from a corewhich is a specially drilled segment of rock removed by special toolsfrom a predetermined depth in the well) is virtually impossible. Forinstance, it is stated in U. S. Patent No. 2,214,674, at line 46 etseq., column 1, page 3, The routine for testing for gas generally hasbeen to mix gas with air to provide a combustible mixture which can thenbe tested for gas by the conventional hot wire lament method. Thisprocedure for detecting gas has not, however, been successfully appliedto core analysis, due to the fact that the gas will escape from the corewhen it reaches the top of the well due to. the reduction in pressure.That the gas will escape from cuttings in the same manner as from acore, due to a reduction in/pressure, is well recognized by oiloperators, and prior to development of the present invention, it wasthought impossible to successfully test cuttings for gas. However, suchtests can be made in accordance with this invention. A possibleexplanation therefor is that as the mixture of air and an extremelysmall amount of gas, for instance, bubbles over the cuteffect. arelatively high vacuum on the cuttings.

Another possible theoretical explanation is that the cuttings have aselective aflinity for the air; and when air is circulated about thecuttings, the air tends to permeate the cuttings and displace the gastherefrom. It is known, of course. that silica gel has a selectiveainity for moisture or water vapor, whereas finely divided activatedcarbon has a selective afnity for gas rather than water vapor. Applyingthe same reasoning in the present instance, it appears possible that gasbearing cuttings, which are normally sandstone or limestone, orsometimes granular sand, have a selective aiiinity or preferentialabsorption for air rather than a combustible gas, which causes the gasto be displaced from the cuttings by the air during the continuedcirculation and recirculation of the air therethrough. Ordinarily, ofcourse, natural gas consists principally of methane, with relativelysmaller amounts of ethane and propane, along with stilly smaller amountsof higher aliphatic hydrocarbons, such as butane, pentanes, hexanes,heptanes, and octanes. Also, the theoretical explanation of the resultsproduced by this invention may be due to phenomenon not now appreciated.

In any event, whatever the theoretical explanation, the fact of thematter is that sufficient gas can be removed in accordance 'with thisinvention to provide accurate indications thereof, fromcuttings whichwere heretofore considered to be completely dead, as it were, withrespect to any combustible gas still contained therein.

As further evidence that the extraction of gas from the cuttings, whenpresent therein, is apparently due to the partial pressure of the gas,or selective absorption, or to some other phenomenon, and not so much tothe vacuum produced initially, is shown by the variation of Fig. 3. `Asillustrated therein, a by-pass line 50 provided with a valve 5| isinstalled around the compressor `20. When pulling the initial vacuum,the bypass valve 5I is closed, and when the desired vacuum has beenproduced in container I2, the by-pass valve 5| and valve I8 are opened,so that the circulation and recirculation of the air begins. The by-passline 50 is useful in increasing the amount of vacuum initially pulledand in reducing the size and amount of air handled by the compressor,but at the same time permits an adequate circulation of the air over andthrough the cuttings and through the detector filament housing 23. Byuse of by-pass line 50, an initial vacuum of 20l Hg has been produced inan installation wherein only 4 to 5" Hg was previously produced.However, the amount of gas evolved from the same type of cuttings wasonly slightly increased, and not nearly as great as would be expectedfrom the proportions of the degrees of vacuum involved. It will beunderstood, of course, despite theoretical considerations, that theinitial vacuum is highly desirable because it assists materially in therecirculation of the air and produces a dierential in pressure whichcauses more positive recirculation and also causes the recirculating airto pass more vigorously through the cuttings.

The sensitivity of the detection of gas in accordance with thisinvention is very great. In one installation, a full scale reading ofgalvanometer 32, actually indicating only one milliamp,

A was considered to beA one hundred for comparison purposes.

In one instance, a reading of only two to three on the galvanometerscale was sufficient to indicate a gas productive zone. This indicationwas corroborated by the fact that the well was a good gas producer.

Testing of the' cuttings for gas, in accordance with this invention, andfor oil as ancillary thereto, may be at intervals, when theSub-structure is fairly well known, or, in th/e case of va Wildcat orexploratory Well, numerous tests may be made. This invention isparticularly applicable to exploratory wells, since no special tools forbringing up cores are needed, and testing does not interfere at all withnormal drilling operations.

When either oil or gas, or both, are indicated by testing as describedabove, and particularly when the geological formation appears lto becapable of actually producing the oil or gas present, the well may betested by what is termed a drill stem test. In this test, the drillstring or pipe is pulled and a special test tool placed on the end ofthe drill pipe. This special tool is lowered to the desired level, andan expanding packer is actuated to seal that portion of the well belowthe packer from the portion above. Of course, when the drill string ispulled there will be no mud left in the drill string, and the pressurebelow the packer will be normal atmospheric, for the elevation at thatpoint. Thus. instead of 3,000 lbs. per sq. in. at a depth of 6,000 ft.,for instance, the pressure will be only slightly greater than normalatmospheric. Gas or oil in the particular section involved will forcemud remainingr below the packer un through thepipe and the oil and gaswill then enter the pipe and it will soon be known whether or not thewell is a producer. Sometimes. in the case of limestone or otherformations. which are low in permeability, acidizing or shootingl theformation may be necessary before it will produce. From the foregoing,it will be evident that this invention fulfills to a marked degree therequirements and objects hereinbefore set forth. The apparatus necessaryfor testing for gas is relatively inexpensive. and easily transported.The operation thereof is fairly simple. and there are substantially noparts which will tend to give trouble. Also. no auxiliary drillingequipment is needed, and there is no interference with normal drillingoperations. The test may be repeated as often as desired, as indicatedby the type of l structure evidenced by the cuttings and any othergeological data which may be available.

While the method of this invention has been described as carried out bya particular type of apparatus, it will be understood that variouschanges, both in the method and apparatus, may be made. Thus, while theelectrical detection of gas has been described specifically, Vit will beunderstood that the presence of gas may be ascertained in some othermanner, as by chemical analysis. It will further be understood thatadditional embodiments of this invention may exist and that variouschanges also may be made therein, all without departing from the spiritand scope of this invention] What is claimed is:

1. A method of gas detection in connection with a well, which comprisesseparating cuttings from mud and the like; placing a predeterminedamount of cuttings in a closed container; introducing air into the lowerportion of said container, whereby such air moves upwardly in saidcontainer to contact said cuttings; removing said air from the upperportion of said container; recirculating the same air through saidcontainer and cuttings, and including gas which is removed from saidcuttings; and testing said recirculating air for gas.

2. A method of gas detection in connection with a well, as defined inclaim 1, which includes agitating said cuttings.

3. A method of gas detection in connection with a well, which comprisesseparating cuttings from mud and the like at the upper end of said well;immersing a predetermined amount of cuttings in a predetermined amountof water, in a container adapted to be closed; introducing air into thelower portion of said container, whereby such air moves upwardly in saidwater to contact said cuttings; removing said air from the upper portionof said container; recirculating the same air through said container andcuttings, and including gas which is removed from said cuttings; andtesting said recirculating air for gas.

4. Apparatus for detection of gas in cuttings separated from mud and thelike from a well, comprising a closed container for receiving apredetermined amount of said cuttings; means for introducing air intothe lower portion of said container, whereby such air contacts saidcuttings; means for removing said air from the upper portion of saidcontainer; means for recirculating the same air through said containerand cuttings, and including gas'which is removed from said cuttings; andmeans for testing said recirculating air for gas. l

5. Apparatus for detection of gas in cuttings separated from mud and thelike from a well, as defined in claim 4, including means for agitatingsaid cuttings.

6. Apparatus for detection of gas in cuttings separated from mud and thelike from a well, comprising a container for immersing a predeterminedamount of cuttings in a predetermined amount of water, said containerbeing adapted to be closed; means for producing a pressure lower thanatmospheric within vsaid container; means for agitating said cuttings;means for introducing air into the lower portion of said container,whereby such air moves upwardly in said water to Contact said cuttings;means for removing said air from the upper portion of said container;means for recirculating the same air through said container andcuttings, and including gas which is removed from said cuttings; andmeans for passing said recirculating air, including removed gas, to adetector adapted to produce an indication of the presence of acombustible gas in said recirculating air, and back to said container.

'7. In apparatus for detecting gas in cuttings removed from a well andseparated from mud or the like, a closed container for a portion of suchcuttings; an air circulator for removing air and air-gas mixtures fromsaid container; a recirculation line leading from said circulator tosaid container at a point spaced from the connection point of saidcirculator; and an impeller for agitating the cuttings in saidcontainer.

8. In apparatus for detecting gas in cuttings removed from a well andseparated from mud or the like, a closed container for a portion of suchcuttings; an air circulator for removing air and air-gas mixtures fromsaid container; a detector adapted to indicate the presence of anair-gas mixture of predetermined concentration; a housing for saiddetector; an air and air-gas line vleading from said air circulator tosaid housing;

a recirculation line leading from said housing to said container; arecirculation tube extending to the lower portion of said container; animpeller for agitating the cuttings in said conl1 tainer; and a valvedby-pass line extending around said circulator.

9. Apparatus for detecting gas from cuttings removed from a well andseparated from mud or the like, comprising a container adapted toreceive a portion of such cuttings and liquid in which said cuttings areimmersed; an air circulator for removing air and air-gas mixtures fromsaid container; a cap for said container having a valved inlet and avalved outlet, with a recircu-` lation tube extending to the lowerportion of said container from said inlet; a suction tube connectingsaid outlet with the intake of said air circulator; a detector adaptedto indicate the presence of an air-gas`nxixture of predeterminedconcentration; a housing for said detector; an air and air-gas pipeleading from the exhaust side of said air circulator to said housing; arecirculation tube leading from said housing to said container inlet; animpeller for agitating the cuttings in said container: and a valvedbypass linel extending around said circulator.

` 10. In the detection of gas in cuttings from a well, the steps whichcomprise separating cuttings from mud and the like at the upper end ofsaid well; placing a predetermined amount oi cuttings in an enclosedspace; producing a pressure lower than atmospheric within said space;introducing air into the lower portion of said space, whereby such aircontacts said cuttings; removing said air from the upper portion of saidspace; and recirculating the same air through said space and cuttings,including gas which is removed from said cuttings, whereby said recirculating air may be tested for gas.

11. In the detection of v gas in cuttings from a well. the steps whichcomprise separating cuttings from mud and the like at the upper end ofsaid well; immersing a predetermined amount of cuttings in apredetermined amount of water, in an enclosed space; producing apressure lower than atmospheric within said space; agitating saidcuttings; introducing air into the lower portion of said space, wherebysuch air moves upwardly in said water to contact said cuttings; removingsaid air from the upper portion of said space; and recirculating thesame air through said space and cuttings, and including gas which isremoved from said cuttings, whereby said recirculating air, includingremoved gas. may be tested for the presence of a combustible gas.

12. In apparatus for detecting gas in cuttings removed from a well andseparated from mud or the like, a closed container for a portion of suchcuttings; an air circulator for removing air and air-gas mixtures fromsaid container; a detector for indicating the presence oi' a combustiblegas; a recirculation line extending between said circulator, saiddetector and said container; and a recirculation tube connected withsaid recirculation line and extending to the lower portion of saidcontainer.

13. In apparatus for detecting gas in cuttings removed from a well andseparated from mud or the like, a closed container for a portion of suchcuttings; means for agitating cuttings in said container; an aircirculator for removing air and air-gas mixtures from said container; adetector for indicating the presence of a combustible gas; arecirculation line connecting said circulator and said detector withspaced points f Said contai-ner; and a valved by-pass line extendingaround said circulator.

14. A method of gas detection in connection with a well, which comprisesseparating cuttings s from mud and the like at the upper end of saidwell; placing a predetermined amount of cuttings in a container adaptedto be closed; producing a pressure lower than atmospheric within saidcontainer; introducing air into the lower portion of said container,whereby such air con-f tacts said cuttings; removing said aixl from theupper/portion of said container; recirculating the same air through saidcontainer and cuttings, and including gas which is removed from saidcuttings; and testing said recirculating air for gas.

15. A method of gas detection in connection with a well, which comprisesseparating cuttings from mud and the like at the upper end of said tingsin a predetermined amount of water, in a container adapted to be closed;producing a pressure lower than atmospheric within said container;agitating said cuttings; introducing air into the lower portion of saidcontainer, whereby such air moves upwardly in said water to contact saidcuttings; removing said air from the upper portion of said container;recirculating the same air through said container and cuttings, andincluding gas which is removed from said cuttings; and passing saidrecirculating air, including removed gas, to a detector adapted `toproduce an indication of the presence of a coinbustible gas in saidrecirculating air.

16. A method of gas detection in connection with a well, which comprisesseparating cuttings from mud and the like at the upper end of said well;immersing a predetermined amount of cuttings in a predetermined amountof water, in a n container adapted to be closed; closing said container,thereby trapping air above the water; agitating said water and saidcuttings; removing air from said container and circulating the samearound a closed path which initially contains air and leads back to saidcontainer. said circulating air thereby picking u p gas released fromsaid cuttings; and testing said circulating air for gas.

JACK E. BLISS. OLIN R. PRATHER.

vREFERENCES CITED The following references are of record in the ille ofthis patent: f

UNITED STATES PATENTS Number Name Date 490,508 Shaw Jan. 24, 18931,725,925 Kent Aug. 27, 1929 1,933,734 Hornung Nov. 7, 1933 6 2,110,319shayes et a1. Mar. 8, 1938 2,142,270 Vander Henst Jan. 3, 1939 2,183,763Brown Dec. 19, 1939 2,213,138 Hayward Aug. 27, 1940 2,214,674 HaywardSept. 10, 1940 2,229,884 chalkley Jan. 28, 1941 2,231,166 Knoedler Feb;11, 1941 2,263,108 Stuart Nov. 18, 1941 2,341,169 Wilson et al. Feb. 8,1944 2,361,137 Terry et al. Oct. 24,1944 2,369,811 stuart Feb. 2o, 19452,376,221 Baker May 15, 1945 well; immersing a predetermined amount ofcuti

